This invention relates to a method for molding a single-piece plastic shell having a pliable outer skin layer backed by a soft foam layer.
U.S. Pat. No. 5,238,622 discloses a method for molding a plastic shell from a self-skinning foamable thermoplastics material which, when cast against a heated mold surface, produces a non-porous outer skin layer backed by a thin layer of soft foam material. The concurrent development of the skin and foam backing layers simplifies the manufacturing of the shell by combining what otherwise would be separate steps in the formation of the skin layer and foam backing layer. It has been found that when the skin layer portion of the shell is made very thin (i.e., on the order of 0.001 inches to 0.010 inches) and somewhat porous, that the panel exhibits a desirable tactile gripping quality that is very pleasing to the touch making it desirable for use in automotive interior applications such as door panels, arm rests, and the like. However, it has further been found that such a thin and porous skin layer is far less durable and wear resistent than conventional dense and non-porous skins frequently used in such applications, such as the materials disclosed in U.S. Pat. No. 4,562,025.
A foam-backed plastic shell formed in accordance with the present invention overcomes the foregoing objections.
A method of molding a plastic shell having an outer pliable skin layer and a foam backing layer includes providing a charge of wear resistant material and a separate charge of self-skinning foamable material. In a first casting sequence, the wear resistant material is cast against only a portion of a heated mold surface of a casting mold to form a first-cast portion of the shell""s outer skin layer. In a subsequent casting sequence, the self-skinning foamable material is cast against the remaining portion of the mold surface still exposed after the first casting sequence and over the first-cast portion of the outer skin layer to generate simultaneously a remaining portion of the outer skin layer that is united to the first-cast portion thereof and an integral foam backing layer that extends across the entire skin layer of the shell.
A primary advantage of the present invention is that the majority of the shell can be made from the self-skinning foamable material having an outer skin layer that exhibits the tactile gripping quality desirable in automotive interior trim applications discussed above. In those regions of the shell susceptible to high wear, such as the tops of arm rests and other areas contacted frequently by the user or objects supported by the shell, such as cup holders, trays, and the like, a relatively greater wear resistent (preferably non-foaming for the greatest wear resistance) material can be employed to provide the skin layer in such high wear regions of the shell.
The present method retains the advantages provided by the self-skinning foamable material in eliminating the need to first form an outer skin layer and then a separate foam backing layer in separate operations, while overcoming the wearability disadvantages of a thin skin layer of such self-skinning foamable material by incorporation of a relatively more durable skin layer portion of wear resistant material in regions of the panels susceptible to high wear.
According to yet another advantage of the invention, the wear resistant material can be colored differently than the self-skinning foamable material to generate a one-piece multi-color skin layer on the shell.